What is a fen and why is this research project happening?

The unique geological and environmental beauty of Pound Ridge, etched by the icy fingers of the glaciers into stunning rocky woodlands and intricate networks of wetlands and streams, gives rise to some rare areas called calcareous fens. Three such fens are located at the Pound Ridge Land Conservancy’s Isaacson Preserve, which was donated by Joe and Evelyn Isaacson in 1981 and 1985.

A fen is a floating mat of sedge vegetation with an inflow of cold, alkaline groundwater. The groundwater is alkaline due to its passage through calcium-rich bedrocks such as the marble bedrock found in Pound Ridge. The fen environment is home to rare plants which thrive in alkali conditions.

Phragmites australis is an invasive reed whose purple seed fronds are seen along many highways and roads at this time of year. Although beautiful in its own right, P. australis takes over wetlands by outgrowing native plants both in height and vigor. In the fall of 2005, Dr. Kearns visited the Isaacson Preserve with other members of the PRLC board and two members of the Westchester Land Trust. She estimated that P. australis occupied approximately 0.75 acres near and in the fen areas, and she joined in the concern that P. australis might overwhelm the fragile fen ecology, which happily still contained many sedges and other native fen plants, as well as fauna such as blue herons, wild turkeys, snapping turtles, and a myriad of colorful dragonflies.

Background for the Research Plan

The research plan for containment is based on information from the Element Stewardship Abstract for Phragmites australis authored by Marianne Marks, Beth Lapin, and John Randall in 1993 for The Nature Conservancy in cooperation with The International Network of Natural Heritage Programs and Conservation Data Centers. In this abstract, a method for controlling P. australis by cutting the reeds in late July is discussed. The concept is that the plant’s carbon will be sequestered in the reproductive parts of the reed at the height of the photosynthesis season, and that cutting the reeds at the first leaf node will remove the carbon before it is transported back to the rhizomes for energy storage in preparation for winter. Lacking carbon sources for the winter, the rhizomes will be weakened or die, and the spread of the reed will be curtailed.

The Element Stewardship Abstract described a number of instances in which the cutting method was successful. The cutting method, used at the correct phase of the photosynthesis season in late July and with care to remove the cut material away from the wetland areas to avoid reintroduction to the site, was successful in eliminating the reed colony if carried out for several years (Osterbrock 1984 and Schnieder, pers. comm. 1990, as cited in the abstract). “In Connecticut, cutting below the first leaf at the end of July in 1986, 1989, 1990, 1991, and 1992 in a freshwater tidal wetland around the perimeter of a one-acre patch has prevented subsequent expansion of the patch. Monitoring using aerial photos taken at five-year intervals indicated the control success…In a second area, similar efforts in a calcareous wetland 1990-1992 were monitored by placing red survey wires around the perimeter of the patch. Preliminary observations indicate a cessation of Phragmites expansion.” And finally the Element Stewardship Abstract states that,”in Europe, Weisner and Graneli (1989) found that oxygen transport was reduced by cutting culms above and below the water surface; cutting below the water surface in June almost totally inhibited regrowth of shoots the following summer. Cutting in sandy substrates was minimally effective, while cutting on calcareous muds caused decreases in oxygen levels”

Oxygen transport is connected to photophosphorylation and the production of ATP, an energy related molecule. So, cutting appears to affect not only the actual long-term carbon status of the plant, but also its production of short-term energy in the form of ATP.

Research Details

The cutting method takes advantage of the well-documented natural plant metabolic processes of seasonal carbon flux, rather than relying on potentially harmful chemicals such as Round Up. The PRLC board, after careful consideration, voted to begin research on the efficacy of cutting Phragmites australis starting in late July 2006. The PRLC board believes this natural cutting approach most closely aligns with the intents of the donors of the Isaacson Preserve who were greatly concerned with water quality in Pound Ridge. The NYS-Department of Environmental Conservation gave its approval on July 5, 2006, and the project began on July 25, 2006.

The volunteer research project is headed by Dr. Ellen V. Kearns, PhD.

  • The perimeters of the P. australis colonies in the Isaacson Preserve were marked and five plots were established in late July 2006 to monitor efficacy of cutting.
  • Cutting was completed with flat hedge trimmers and black plastic bags of cut material were removed to dry, high ground to avoid reintroduction of P. australis to the site. In 2008, 48 thirty-gallon bags were removed.

 

Results for 2008

The results of 2008 show significant decrease in individual height and diameter of P. australis in all plots (Chart 1 and Chart 2).

Chart One: Height of P. australis individuals in research plots decreasing over three years of cutting.

Chart Two: Diameter of P. australis individuals in research plots decreasing over three years of cutting.

The number of individual P. australis showed significant decrease in every plot except Plot 4, where 18 individuals appeared tiny and grass-like (Chart 3).

Chart Three: Number of P. australis individuals in research plots decreasing over three years of cutting, except in Plot 4 at the periphery of the meadow Fen1, where individuals are becoming grass-like.

White flag markers at the edge of Fen 2 show that the periphery is receding and Fen 3 is still P. australis free.

Summary

The cutting protocol described here appears to have real impact on the Phragmites australis in the Isaacson Preserve. All parameters measured, height, diameter, and number of individuals, are down in this third year of cutting, except in Plot 4, where the appearance of grass-like individuals continues to increase the total number of individuals. It is not clear whether these grass-like individuals are badly stressed P. australis or another species. The project will continue to cut and monitor for at least another two years in which it may be possible to completely remove P. australis from Fen 1.

Research Credentials

Dr. Kearns wrote her undergraduate thesis (1986) at Smith College on the genetic lineages of American Chestnut trees in Skinner State Park. She received her PhD from the MSU-DOE Plant Research Laboratory in 1991, and conducted post-doctoral research on environmental responses in Arabidopis thaliana at Harvard’s Organismic and Evolutionary Biology Department (1992-1993), the Department of Biology at Massachusetts Institute of Technology (1993-1995), The Max-Planck-Institut fuer Molekulare Pflanzenphysiolgie in Golm, Germany(1995-1996), and the Department of Biology at Dartmouth College (1996-1998).

Citations from the Element Stewardship Abstract

Juntos, Robert Jr., and Christopher P. Allen. 1984. Test salt to control Phragmites in salt marsh restoration (Connecticut). Rest. and Mgmt. Notes 2(1):32

Osterbrock, A.J., 1984. Phragmites australis. The problem and potential solutions. Ohio Field Office, Stewardship. 8pp.

Schnieder, K. 1991. Coordinator, New York Hertitage Program. Telephone conversation with Beth Lapin. October 1990.

Weisner, W.E.B, and W. Graneli. 1989. Influence of substrate conditions on the growth of Phragmites australis after a reduction in oxygen transport to below- ground parts. Aquatic Biology 35:71-80.

Thank you to Rebecca Crist, whose dedicated review of this project for the NYS-DEC made it possible.